Lesson 4 of 10 / Homeostasis and response
Blood glucose control
How are a glucose rise and a glucose fall corrected?
I can compare the roles of insulin and glucagon in negative feedback.
I can explain insulin and glucagon in glucose homeostasis.Syllabus
Syllabus K325, Topic 8(f). Explain insulin and glucagon in glucose homeostasis.
About 6 min
Make a guess. You are not marked.
You skip lunch and your blood glucose falls. Which hormone is released to raise it?
Show the answer
Glucagon, which makes the liver release glucose.
Glucagon promotes breakdown of liver glycogen into glucose, which enters the blood.
The key idea
Insulin lowers blood glucose by promoting uptake and storage; glucagon raises it by promoting glucose release from the liver.
Arrows show the causal sequence, not the movement of one substance through every box. Glucagon acts on the liver; glycogen is not released into blood.
High blood glucose -> more insulin from beta cells -> more glucose uptake and glycogen formation -> blood glucose falls. The insulin stimulus then decreases.
Explanation
After a carbohydrate-containing meal, absorbed glucose can raise blood glucose concentration. Beta cells in the pancreatic islets release more insulin. Insulin promotes glucose uptake by target cells, especially muscle and fat cells, and promotes conversion of glucose to glycogen in liver and muscle.
Glucose uptake and storage remove glucose from the blood, so its concentration falls towards the usual range. As the original rise is corrected, the stimulus for increased insulin secretion becomes smaller. This is negative feedback.
Between meals, blood glucose may fall. Alpha cells in the pancreatic islets release more glucagon. Glucagon acts on the liver, promoting the breakdown of stored glycogen to glucose and the release of glucose into the blood.
Blood glucose then rises towards the usual range and glucagon secretion decreases. Insulin and glucagon have opposing effects on the regulated condition. Muscle glycogen is a local fuel store; do not describe glucagon as making muscle release its glycogen as glucose into the blood.
Step by step
- 1
Choose the hormone
A rise stimulates more insulin; a fall stimulates more glucagon.
- 2
Explain target action
Name glucose uptake or glycogen formation for insulin, and liver glycogen breakdown for glucagon.
- 3
Return to the variable
State how blood glucose changes and why hormone secretion then decreases.
Worked example
Between meals
Blood glucose falls between meals. Explain a response that restores it.
One way to explain it
Pancreatic alpha cells release more glucagon. It promotes glycogen breakdown in the liver, which releases glucose into blood. Blood glucose rises towards normal, reducing the stimulus for glucagon secretion.
Why this answer works
- Begin with a fall, so choose glucagon.
- Locate glycogen breakdown and glucose release in the liver.
- Close the negative-feedback loop.
Watch out for this
A student says: "Insulin turns into glucose, while glucagon turns into glycogen." What is wrong with this?
Show the answer
Both are hormones that signal changes in target-cell activity. Glucose and glycogen are the substances interconverted during storage and release.
Check your understanding
Which response directly helps correct low blood glucose?
Show the answer
Glucagon promotes liver glycogen breakdown and glucose release.
The liver releases glucose, raising blood glucose towards its normal range.
Exam-style questions
Check your understanding
After a meal, a person's blood glucose rises from 5 to 8 mmol/dm3 and returns to 5 within two hours. Which hormone mainly brings it back down, and how?
Show the answer
Insulin, by making liver cells convert glucose to glycogen
Insulin is released when glucose rises and causes the liver to store glucose as glycogen.
Quick recall
How are a glucose rise and a glucose fall corrected?